Columbia University researchers studied the blood samples of nearly 6,000 people. They found two genotypes with the strongest association to Alzheimer's disease among African-Americans: ABCA7 and APOE.

These two genotypes have also been linked to an increased risk for developing Alzheimer's disease among people of European ancestry, too.

"So, we know that different races and different ethnicities have different risk factors for different diseases. And we now know that that may be a slightly different genetic risk for African-Americans compared to white ancestry," said Dr. Brian Appleby, of the Cleveland Clinic.

Researchers say the discovery could lead to Alzheimer's treatment and prevention methods down the road, but more studies are needed.

"Even if you have that 'risk gene' it doesn't mean you're going to get Alzheimer's, and in fact, a lot of people that don't have these risk genes get Alzheimer's. So, it's not really useful for diagnosis, but it may be helpful in trying to come up with different diagnostic tests and probably, more importantly, treatment responses in the future," Appleby said.

The complete findings are in the Journal of the American Medical Association.